1. Field of the Invention
The invention relates to a device and method for determining and communicating the remaining life of a battery or other power source in a device for electrically stimulating neurological tissue.
2. Description of Related Art
Implantable devices exist that electrically stimulate neurological tissue to treat or relieve the symptoms of a wide variety of physiological or psychological maladies or pain. Such devices are typically part of systems that are entirely implantable within the patient or are partially implantable and partially external to the patient. Systems that are entirely implantable in the patient typically include an implantable pulse generator (IPG) and an extension and lead or leads. In such a system, the IPG, extension and lead are entirely implanted in the bodies of the patients. An example of such a system is the Itrel(copyright) 3 system manufactured and sold by Medtronic, Inc. of Minneapolis, Minn.
A programmer is used outside the patient""s body and communicates with the IPG by both sending and receiving information to and from the IPG. The programmer is used to set and adjust the system, including the parameters of the stimulation pulses, to be most therapeutically effective. This programmer typically includes a computer, programming head and a printer. The programming head is placed over the IPG to program desired system settings using radiowaves. The programming head also receives information from the IPG such as the current electrical pulse parameters or status information. This procedure is done through the skin.
Because the IPG is implanted, the power sources needed to power the IPG is also implanted. Typically, the power source for an IPG is a battery.
Systems that are partially implantable and partially external to the patient include so called xe2x80x9cradio frequencyxe2x80x9d (RF) systems. An example of such an RF system is the Mattrix(copyright) system manufactured and sold by Medtronic, Inc. of Minneapolis, Minn. This RF system comprises an external transmitter, an antenna coupled to the external transmitter, an implanted receiver and a lead or leads. The receiver and leads are implanted in the patient""s body. The external transmitter generates a series of electrical pulses according to a defined therapeutic pattern. The pulses arc passed to the antenna where they are transmitted to the implanted receiver in the patient""s body. The implanted receiver passes the pulses to the lead or leads where the pulses are applied to the tissue that is to be stimulated.
One main difference between an entirely implantable system and a RF system is the battery location. The totally implantable system uses a battery that is placed beneath the skin so that no part of the system is outside the body. The radio frequency system uses a battery that is worn outside the body to power the system.
The lead, whether in an RF or IPG system, is a small medical wire with special insulation and contains a set of electrodes (small electrical contacts) through which electrical stimulation is delivered to tissue. The lead is implanted in the patient""s body and the electrodes are placed next to the tissue that is desirable to electrically stimulate. The extension is a small cable that is placed under the skin and connects the lead to the IPG.
Many systems, both IPG and RF, allow the patient to partially control their electrical stimulation through a device known as a patient programmer. The patient programmer is a hand-held device that allows the patient to change or control their electrical stimulation within preset bounds. This device allows the patient to adjust the electrical stimulation using radio waves between visits to the doctor.
FIG. 1 schematically shows an implantable system such as the Itrel(copyright) 3 system including a programmer. As can be seen, the system, generally labeled 2 has an IPG 4, an attached extension 6, a lead 8 attached to extension 6 and an external programmer 10. The IPG 4 has a battery 12 that powers the device and provides the power for the electrical stimulation pulses that are provided to the lead 8 through extension 6 to be applied to the tissue that is to be electrically stimulated. IPG 4 also has a battery voltage determining system 13 that determines the voltage of battery 12.
IPG 4 also includes an IPG telemetry system 14 that receives information from the programmer telemetry system 16 of the programmer 10. Through programmer telemetry system 16, programmer 10 sends commands to the IPG 4 through the IPG telemetry system 14 to change the parameters of the stimulation pulses produced by the IPG 4. In return, IPG 4, through IPG telemetry system 14, sends information to programmer 10, through the programmer telemetry system 16, regarding the current status of the IPG 4 including current parameter settings and the voltage of the battery 12.
In the Itrel(copyright) 3 system, the battery is a Lithium Thionyl Chloride battery. FIG. 2 shows the voltage versus capacity chart for this type of battery. As can be seen, the battery voltage remains virtually constant through most of the life of the battery. At approximately the last 5% of battery life, the battery voltage drops rapidly. Therefore, by tracking the battery voltage, it can be determined that the battery is in its last 5% of life when the voltage drops rapidly. Unfortunately, because the battery voltage is virtually flat for the first 95% of battery life, it is difficult if not impossible to determine where in the battery life cycle the battery is during the first 95% of battery life.
As stated above, IPG 4, through IPG telemetry system 14, sends information to programmer 10, through the programmer telemetry system 16, regarding the voltage of the battery 12. The physician takes this battery voltage information and consults a xe2x80x9clook-upxe2x80x9d table showing battery voltages and corresponding remaining battery capacity values. While the battery voltage is xe2x80x9chighxe2x80x9d and constant, as during the first 95% of battery life, the physician is only able to determine that the battery is somewhere in its first 95% of life. Only when the battery voltage begins to drop can the physician ascertain that the battery is in the last 5% of its life.
Many batteries have battery capacity versus voltage profiles similar to that shown in FIG. 3. As can be seen, these profiles are not xe2x80x9cflatxe2x80x9d along a substantial portion of the battery life. Instead, there are distinct values correlating the measured battery voltage and the battery capacity used or remaining. It is highly desirable to have a system that allows the user to ascertain either the battery capacity already used or battery capacity remaining in batteries having battery capacity versus voltage profiles similar to that shown in FIG. 3.
The invention is a device and method for determining and communicating the remaining life of a battery or other power source in an implantable neurological tissue stimulator. Basically, the invention contemplates a method, performed in a system without human intervention, that includes the steps of assessing the voltage of a battery or other power source in an IPG, determining, using the voltage, where in the battery or other power source life cycle the battery or other power source is, and taking action in response to the determination of where in the life cycle the battery or other power source is.
The invention also includes a device that embodies the method described above. The device, which may be either totally resident in an IPG or partially resident in an IPG and partially resident in an external device such as a programmer, measures the power source voltage in the IPG, uses the power source voltage to determine where in the power source life cycle the power source is and takes appropriate action in response to the determination of where in the power source life cycle the power source is. A processor, either on the IPG or in the programmer or patient programmer is the preferred structure for determining where in the power source life cycle the power source is and for directing the appropriate action in response to the determination of where in the power source life cycle the power source is.
It is therefore a primary object of the invention to provide a device that determines the current status and remaining life of a power source in an implantable neurological tissue stimulator.
It is therefore a primary object of the invention to provide a device that determines the current status and remaining life of a power source in an implantable neurological tissue stimulator without immediate human intervention.
It is therefore a primary object of the invention to provide a device that after determining the current status and remaining life of a power source in an implantable neurological tissue stimulator, automatically alerts the physician to the current status and remaining life of the power source.
These and other objects of the invention will be clear from the description of the invention given herein and particularly with reference to the attached drawings and the Detailed Description of the Invention. Throughout this description, like reference numbers refer to like elements.